In some wireless local area network (WLAN) deployments, such as enterprise deployments, there is a high density of access points (APs). For example, the AP-to-AP spacing can be less than 30 feet to restrict the maximum number of clients per AP. Such deployments have strong AP-to-AP co-channel interference, especially in the 2.4 GHz radio frequency band with only 3 non-overlapping 20 MHz channels.
Newer WLAN standards, such as IEEE 802.11n and IEEE 802.11ac, allow for APs to transmit multiple spatial streams simultaneously to a client, and thereby improve the throughput to that client. In a high density WLAN deployment, one and two spatial stream downlinks are optimal due to the number of 1×1 (single antenna, single transmitter and single receiver) and 2×2 (two antennas, two receivers and two transmitters) devices in use (e.g., WLAN-capable phones and low/mid-tier laptops) in far excess over the higher tier 3×3 (three antennas, three receivers and three transmitters) laptops needed for three spatial stream performance. High density networks are naturally biased toward one or two spatial stream operation.
It is common to set AP transmit power high in order to provide good downlink signal-to-noise ratio (SNR) at the client. Higher transmitter power also increases AP-to-AP co-channel interference. The AP-to-AP co-channel interference causes the adjacent AP to hold off from making a downlink transmission, according to energy detect clear channel assessment and/or the receiver in the adjacent AP starting to decode the co-channel AP's signal. In addition, if the adjacent AP is attempting to decode an uplink frame, the interference may degrade signal-to-interference-plus-noise ratio (SINR) and result in an increase forward error correction. As a result, AP transmit power is set lower to avoid AP-to-AP co-channel interference, sacrificing the quality link from the AP to its client.